High frequency window structure



Dec. 11, 1956 s. T. MARTIN ET AL 2,773,289

HIGH FREQUENCY WINDOW STRUCTURE Filed May 6, 1949 -J INVENTORJ; A .9 SZLLGI'iT/Wdf'ltl) 7 Mal shall C. Pease l IE I I .ar frffi ATTURIV S)" United States Patent HIGH FREQUENCY WINDOW STRUCTURE Stuart T. Martin, Dedham, and Marshall C. Pease, Ncedham, Mass., assignors to Sylvania Electric Products Inc., a corporation of Massachusetts Application May 6, 1949, Serial No. 91,728 Claims. (CI. 20-40) hermetically sealed to the frame. The glass ordinarily .is hard for high efficiency of electrical transmission, and

the metal is of an alloy having a temperature coelficient of expansion as nearly identical to that of the glass as possible. The metal and the glass are commonly assembled in a furnace where both are heated to the fusion temperature of the glass for sealing it to the metal. Then the window is gradually cooled and is (except for optional surface grinding of the glass) ready for installation.

The window is commonly soldered or brazed to the end of a section of waveguide and enclosed peripherally in a flange. Hard solder is desirable but this uniting operation has the effect of causing thermal stresses that tend to crack the glass center of the window. Similar stresses are also developed during the use of the Window, especially when the equipment is exposed to a latitude of temperature conditions.

The present invention provides means for mitigating the transmission of stresses to the glass in rectangular Windows where the tendency to transmit unbalanced stresses to the glass is particularly troublesome. An oval yielding connection is provided between the outer frame portion of the window and a metal center panel in which the glass is mounted.

The invention will be better appreciated and more completely understood from the following detailed disclosure of various embodiments thereof. In the acompanying drawings:

Fig. 1 is the end view of an assembly of a high-frequency window and a flange in accordance with the prior art and Fig. 2 is an enlarged sectional view along the line 2-2 in Fig. 1;

Fig. 3 is a plan view of a rectangular window embody ing the present invention and Fig. 4 is a sectional view along the line 4-4 in Fig. 3;

Figs. 5 and 6 are views corresponding to Fig. 4 of modified embodiments of the invention; and

Fig. 7 is a graphical aid to the full disclosure of the invention.

In Figs. 1 and 2 there is shown a flange 10 within which a composite metal and glass window 12 is enclosed. The window is rectangular, and of the same size and shape as the end of waveguide 14 to which it is assembled. A difference in gas pressure is established, in use, between opposite surfaces of the window so that the joints between the flange, the window, and the waveguide are usually soldered so as to make them pressure-tight. Hard soldering, involving high-temperatures, is preferred for this purpose. After application of the solder and during cooling there is a tendency of the flange to contract, applying an inward stress that tends to bow and crack the I 2,773,289 Patented Dec. 1 1, 1956 window in the direction indicated by the dotted lines in Fig. 2. The tendency of cracking is particularly serious with rectangular windows where the stresses are not circularly symmetrical.

In Figs. 3 and 4 one form of improved window is shown for protecting the glass against stresses imposed at its periphery. A central glass area 18 is sealed in the metal frame 16, being supported on a central panel 20 supported by integral yielding connection 22.

The contour of yielding connection or dimple 22 is shown in Fig. 3, and a family of like contours is shown in Fig. 7 for rectangular windows whose sides have a ratio of 1:2. The contour of the yielding connection is such that stresses resulting from compression applied at the edges of the rectangle will at all points be perpendicular to the yielding connection. By this device, twisting stresses that would inevitably crack the glass are not developed in the central panel, and the strains tending to produce bending moments in the glass are largely absorbed by the yielding connection itself. The contoursof the connection may be expressed mathematically as:

Sin H sin -=A a b where a and b are the dimensions of the rectangular piece of metal and A is a constant which determines the particular contour used. The terms x and y are the variable ordinates and abcissae of the curves. With values of A varying from 0.1 to 0.9, the family of curves is obtained that appears in Fig. 7. The various curves obtainable with different values of A make different spaces available for the apertured central panel within. which the glass is sealed. .As mentioned above, the yielding connection is of such contour that any stress applied perpendicularly to the rectangular edge is transmitted so as to be perpendicular to the yielding connection, where that connection corresponds to one of the family of curves derived by the formula given. This shape may be described as oval, and is curved everywhere but is of varying curvature from point to point along any curve with any chosen value of A.

In Figs. 3 and 4 the yielding connection is shown in the form of a dimple that is drawn out of a flat metal sheet that forms frame 16. The connection may be of reduced wall thickness as compared to the fiat portions of the metal sheet. The window is seen in Fig. 4 to be cupped, with the glass supported in a central panel of metal joined by the yielding connection of the above contour that is generally oval to the outer frame portion. In Fig. 5 another form of drawn or struck-up yielding connection is shown in which the glass is in the same plane as the frame, primed numerals being applied to the several parts corresponding to Fig. 4. The yielding connection 22' is in the form of a corrugation. In Fig. 6 another form of window is shown in which the central panel 20" is soft-soldered to the outer frame portion 16" in a yielding connection 22" that follows the prescribed contour. In all three forms of window, the same characteristic is present: the yielding connection follows a contour a connection in which the stresses applied at the edges and propagated toward the central panel are perpendicular to the contour of the yielding connection, and the glass supported on the central panel is shielded from cracking stresses.

The several forms of windows illustrated are adapt-able to different uses, depending upon electrical considerations. The windows of Figs. 4 and 5 have a flat surface produced by grinding, to the end that the amount of glass remaining will produce the calculated effect on the transmitted wave, and these provide for a very substantial degree of yield.

The window of Fig. 6 is formed of two different metal portions 16" and 20", both desirably being of the same metal so as to have substantially the same temperature coefficient of expansion. This particular arrangement, in connection with circular windows, is covered in copending application Serial No. 57,238 filed October 29, 1948, by Louis C. Remond, and which became Patent No. 2,744,592 on May 8, 1956.

Thevarious embodiments of the invention described above will be recognized as being capable of varied app-lication and modification by those skilled in the art. It is therefore appropriate that the appended claims be accorded that broad interpretation as is consistent with the spirit and scope of the invention.

What is claimed is:

1. A window having a substantially fiat rectangular metal frame, an apertured central metal panel, a glass closure sealed to the edges of the aperture, and an oval yielding connection between said frame and said panel.

2. A window having a susbtantially fiat rectangular metal frame, an aperture central panel carrying a glass closure sealed to the edges of the aperture in the central metal panehand a yielding connection between the frame and the panel having a contour according to the following expression:

A =sin 7E sin Ly where a and b are the sides of the rectangle, where x and v are the variable ordinates and abcissae defining the various points along the curve, and A is a constant.

' 3. A window having a susbtantially flat rectangular metal frame, an aperture central metal panel, a closure of glass or the like sealed to the edges of the aperture in the central panel, and an oval yielding connection interposed between said metal frame and said metal panel and extending out of the plane of the susbtantially fiat metal frame.

4. A window having a substantially flat rectangular metal frame, an apertured central metal panel, a closure of glass or the like sealed to the edges of the aperture, and a yielding oval corrugation interposed between and joining said frame and said central panel.

5. A device including a rectangular waveguide and a rectangular window united at its edges to said waveguide, said window having a susbtantially flat rectangular metal frame, an apertured central metal panel, a closure of glass or the like sealed to the edges of the aperture in the central metal panel, and an oval yielding connection between the flat metal frame and the central metal panel, said device being hermetically sealed and having a difference of gas pressure at opposite surfaces of the window.

References Cited in the file of this patent UNITED STATES PATENTS 2,050,576 Kronquest Aug. 11, 1936 2,075,477 Smith Mar. 30, 1937 2,219,574 Fraenckel Oct. 29, 1940 2,454,741 McCarthy Nov. 23, 1948 2,467,730 Coltman Apr. 19, 1949 2,533,512 Samuel Dec. 12, 1950 2,534,392 Walsh Dec. 19, 1950 2,584,653 Alpert Feb. 5, 1952 FOREIGN PATENTS 583,242 Great Britain 1946 

